(1) Field of the Invention
The present invention relates to an abrasion-resistant granular zeolite and a process for the preparation thereof. More particularly, the present invention relates to an improvement for increasing the abrasion resistance of a granular zeolite without reduction of the zeolitic characteristics of the zeolite.
(2) Description of the Prior Art
A synthetic zeolite is valuable as a drying agent, a molecular sieve, an ion exchanger or a catalyst carrier. However, the synthetic zeolite per se is a very fine crystalline powder having no binding property, and in order to convert this powder to a granule which is easy to handle, it is necessary to mix this powder with a clay binder such as kaolin, attapulgite or allophane and granulate the mixture.
In order to improve the mechanical properties, such as the compression strength, of the so prepared granular zeolite, it is necessary to incorporate a considerably large amount of the clay binder into the zeolite powder, and therefore, reduction of the zeolitic characteristics such as the adsorbing characteristic and ion exchange capacity is readily caused. Therefore, the mixing ratio of the clay binder has heretofore been controlled within the range of 20 to 30% by weight so as to maintain a good balance between the zeolitic characteristics and the mechanical strength characteristics.
In various application fields of granular zeolites, however, it is always required to improve the mechanical strength characteristics, especially the abrasion resistance and compression strength, without reduction of the zeolitic characteristics. For example, a granular zeolite to be used as an air brake drier should have an abrasion resistance sufficient to resist violent vibrations and a water-absorbing property enough to prevent dew condensation, freezing or corrosion in the brake system for a long time should stably be maintained over a long period of time.